Balancing Health and Performance Benefits through Natural Lighting

Understanding how to specify glazing systems that balance access to natural light with thermal performance and building code requirements
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Sponsored by Oldcastle BuildingEnvelope®
By Juliet Grable

Learning Objectives:

  1. Discuss how access to natural light impacts human physiology, health, and well-being.
  2. Describe the properties of heat-treated, laminated, and insulating glass, and provide examples of appropriate applications for each.
  3. Explain how to use U-factors, solar heat gain coefficient (SHGC), and visual transmittance (VT) to specify the right glazing system for an application.
  4. Understand how glazing design can be used to manage building energy use while controlling unwanted glare.
  5. Identify several glazing systems that bring natural light into a building and their advantages over other solutions.


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Access to natural light is critically important to human health and performance; it has been shown to benefit many building occupants, including employees, students, and patients in health-care settings. By using creative design to maximize access to natural light, architects, designers, and engineers play key roles in impacting the long-term well-being of building occupants.

All photos courtesy of Oldcastle BuildingEnvelope®

The Claire T. Carney Library redesign project in Boston leverages curtain wall with architectural and structural glass to illuminate the once dimly lit campus library and transform it into a sustainable benchmark that now acts as the campus “living room.”

Using glass in buildings, whether as part of a new project or a remodel, is an effective way to bring natural light into a space. In addition, glass can reduce energy consumption by reducing the need for artificial lighting and, in some cases, cooling required to offset the heat generated by artificial light. Creative solutions utilizing systems such as window walls and curtain walls, interior glass partitions and walls, skylights, and light shelves can help maximize these benefits. Proper design, planning, and application can ensure effective and successful use of glass in buildings to maximize light while offsetting thermal heat gain, and ensuring occupant safety and code compliance.

Health Benefits of Natural Light

Window walls, curtain walls, skylights, and interior glass partitions can all be used to bring natural light into buildings. In addition, ample glass and glazing can provide more building occupants with views of nature and, in some cases, access to fresh air. All of these— natural light, views of nature, and fresh air—are elements of biophilic design. Biophilia refers to the innate human affinity to the natural world, and biophilic design refers to those elements that connect people to nature, whether a window with a view of nature or a dynamic fountain with trickling water. Increasingly, design professionals are recognizing the benefits of biophilic design and incorporating these elements into their projects.

How Light Interacts with the Human Body

Light enables us to perform visual tasks, but it also affects mood, controls the body’s circadian system, and catalyzes critical chemical reactions in the body, such as the production of vitamin D.

Access to natural light helps regulate the human body’s natural circadian rhythm, which supports metabolic processes and leads to more restful sleep. Through the hormone melatonin, the circadian system regulates cycles of wakefulness and sleepiness. The natural human circadian cycle is close to 24 hours; in fact, “circadian” means “about a day.” When people are deprived of exposure to natural cycles of darkness and light, the production of melatonin is disrupted, as are the cycles of alertness and sleepiness, potentially leading to sleep disturbances. It is especially important to access sufficient daylight in the morning to synchronize the body’s “clock” to the earth’s rotation.

Scientists are uncovering more and more links between adequate sleep and almost every aspect of health and well-being. Not only is adequate sleep required to remain alert and perform well, but sleep affects the body’s ability to fight off infections, cancer, and perhaps even Alzheimer’s disease.

High melatonin levels cause drowsiness, while low levels correlate to a state of alertness. In a normal, healthy person, daylight or artificial light activates the pineal gland and suppresses melatonin. When daylight or artificial light is inadequate, the natural suppression of melatonin doesn’t happen; as a result, the person feels tired and depressed.1

According to researchers, the body responds more strongly to daylight as a cue than to artificial lighting. Daylight includes the full spectrum of wavelengths; by contrast, artificial lighting includes a limited part of the visible light spectrum and typically does not include shorter wavelengths. These shorter wavelengths may be important in regulating the circadian cycles. Full-spectrum light may also provide more efficient lighting for vision, potentially reducing eyestrain.2

The positive impacts of daylighting on building occupants have been documented and quantified in nearly every building occupancy type.

At the Nemours/Alfred I. duPont Hospital for Children in Delaware, a striking arbor-patterned curtain wall helps bring ample natural light deep into patient rooms.

Retail Sales

Imagine shopping in a lofty, light-filled atrium compared to a dingy, low-ceilinged building with fluorescent lighting. Which would you choose? Not surprisingly, studies have shown that daylighting can improve retail sales; what may be surprising is the impact on profits.

In one study, retail giant Wal-Mart built a prototype for a “green” store. Only half of the store was lit using daylighting. However, sales per square foot were significantly higher for departments located in that half. Not only that, but sales in daylit departments of this new store were higher than sales in the same department in other Wal-Mart stores without daylighting.

In a more extensive study, researchers analyzed 73 California chain stores over two years. Of these, 49 were lit with artificial lighting. These 49 stores were retrofitted with skylights and subsequently saw their sales spike by 40 percent. The profits due to the skylight retrofit far outweighed the energy savings.3

Terrapin Bright Green estimates that, in general, skylights statistically increase sales by $1.55 per square foot in grocery stores, clothing outlets, and retail chains across the country. It’s no wonder that successful retailers have “seen the light” and embraced daylighting design.

Healing Benefits

Health-care settings present particular challenges: patients experiencing severe pain or mental distress, staff who work long schedules that are out of sync with the normal human cycles, and an environment characterized by constant noise, artificial light, and interruptions.

Daylight can affect patients through the circadian system, helping reduce depression and improve sleep patterns. Daylight may also lessen agitation, ease the perception of pain, and improve the general well-being of staff.

A seminal study conducted in 1984 by evidence-based design researcher Roger Ulrich found that patients recovering from surgery recovered more quickly if their rooms included views of green space compared to those whose rooms faced out onto a wall.4

In a more recent study, researchers found that in-patients suffering from bipolar disorder who had east-facing rooms spent an average 3.67 fewer days in the hospital compared with similar patients who had west-facing rooms, and a study of heart-attack patients showed that female patients who were treated in sunny rooms left a day earlier than patients in “dull” rooms. In addition, mortality was higher among patients staying in the dull rooms.5

Interestingly, exposure to daylight may reduce perceived pain. Patients who underwent elective spinal surgeries recovered in either the dim side or the bright side of the same hospital unit. Those staying on the bright side were exposed to an average of 46 percent higher sunlight intensity than those on the dim side. These patients reported less stress and less pain; they also took 33 percent less pain medication.5

The Nemours/Alfred I. duPont Hospital for Children in Delaware illustrates how daylighting design can be used in a healthcare setting to benefit patients, staff, and visitors. The hospital offers patient rooms with large windows and views of the outdoors, family solariums for gathering, and an outdoor terrace where patients can enjoy fresh air.

Better Conditions for Learning

In schools, good daylighting may improve student performance, help create a healthier indoor environment, and boost attendance. One often-cited study analyzed the test scores of more than 21,000 students in three school districts in California, Washington, and Colorado. Controlling for other factors, the study found that in one school district, students with the most daylighting in their classrooms progressed 20 percent faster on math tests and 26 percent faster on reading tests compared to students in the least daylit classrooms.6

Another study compared test scores for 1,200 students in three daylit schools in North Carolina to scores in the rest of the county’s school system, as well as to other new schools within the county. According to the study, students who attended daylit schools outperformed the students in non-daylit schools by 5 to 14 percent. Perhaps not surprisingly, students stuck in mobile, windowless classrooms during the same study period saw their test scores drop 17 percent.7

In another study conducted in Alberta, Canada, children attending elementary schools with full-spectrum light were compared to children in classrooms with conventional lighting. The results suggest that the students in the full-spectrum lit classrooms had fewer days of absence per year and enjoyed positive health impacts. For example, daylighting allowed the HVAC system to be downsized, which in turn reduced the noise levels in both the classrooms and library, enhancing the learning environment.

As the same study notes, in most cases, enhancing daylighting does not necessarily add to capital costs, and, in some cases, can even cut them, thanks to the reductions in HVAC equipment and artificial lighting.8

Productivity and Satisfaction

The workplace is often a stressful environment for employees, yet people spend a good part of their waking life working. Being able to access nature while at the workplace may help alleviate some work-related stress and lead to happier, more productive employees.

Heart-rate recovery, or how quickly the heart rate returns to normal after a person is exposed to low-level stress, is one way to measure a person’s reaction to his or her surroundings. For example, in one test, 90 participants were broken into three groups of 30 and instructed to perform mildly stressful tasks such as proofreading. One group was exposed to a glass window with a view of nature; the second group was exposed to a plasma screen bearing an image of that same view; and the third was exposed to a wall that was covered by drapes. The subjects with the view out the window experienced greater heart-rate recovery than the other two groups; in addition, when participants spent more time looking at the glass window, their heart rate tended to decrease more rapidly. Interestingly, the plasma screen didn’t appear to be any more restorative than the blank wall.9 A similar study involving an older office space with poor lighting and air quality to a healthy, daylit office showed a similar impact on physiological stress markers. Occupants in the older office showed higher activation of stress hormones, while those in the newer office reported far fewer headaches.10

Through her extensive research, biophilic design expert Judith Heerwagen has shown that people prefer daylight to artificial lighting sources and that most people would choose to be near a window. In one study, she gathered reasons for this preference: psychological comfort, office appearance and pleasantness, general health, visual health, color appearance of people and furnishings, work performance, and jobs requiring fine observation.11

One study has even quantified the economic benefits of providing employees with views to nature. Employees in the Sacramento Municipal Utility District (SMUD) Call Center showed highly variable rates of productivity, depending on whether they had access to views or not. Those with access to views of vegetation through large windows from their cubicles handled far more calls per hour compared to employees with no view of the outdoors. They also handled calls 6 to 7 percent faster than those with no views. SMUD decided to install operable windows and rearrange workstations so that all employees could access these views. The construction cost $1,000 per employee, but the annual productivity savings averaged $2,990 per employee—an outstanding return on investment.12

Good daylighting design could give companies a competitive advantage, helping them attract and retain employees. In one striking example, ING Bank designed a new headquarters building in Amsterdam, which maximized daylighting and integrated organic art and water features. Once the project was completed, absenteeism decreased by 15 percent, and employees self-reported greater job satisfaction. The bank also saved an estimated $2.6 million annually once the energy system and daylighting units were installed.13


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Originally published in Architectural Record
Originally published in June 2019